After teaching at a New Jersey high school, he moved to Lock Haven, Pa., and taught at Lock Haven University. In 1979, he wrote "Historic Lock Haven: An Architectural Survey."

He was named to the Pennsylvania Historical and Museum Commission and served as a curator of Pennsylvania's Clinton County Historical Society.

Nearly 21 years ago, he left Pennsylvania and moved to Charles Village. He then moved to Original Northwood, a neighborhood in Northeast Baltimore. He occasionally taught a mathematics course at the Community College of Baltimore County at Essex and became fascinated by Baltimore's residential neighborhoods. Friends said he worked in architectural history and preservation, and documented the lives and work of regional architects.

"He was passionate about the history of Baltimore," city planner Eric Holcomb said. "His research was detail-oriented, and he always wanted to get to the bottom of a topic. His mind worked rationally and logically as he captured his data."

In 1998, he appeared before the city's Commission for Historical and Architectural Preservation and argued for including Original Northwood on the National Register of Historic Places.

"The work done in Northwood stands as the pinnacle of professional achievement," he said, adding that community had a "clarity of design."

Mr. Wagner described the neighborhood in a 1998 Baltimore Sun article as a "110-acre garden suburb ... conceived as a place where the mix of homes was both expensive and comfortably affordable. Virtually every dwelling was carefully designed by an architect who made adroit use of class-A building materials."

Mr. Wagner also researched Baltimore architect John A. Ahlers, who laid out Original Northwood's curving streets and designed many of its homes.

"Ahlers was a genius for color and design. He must have stood at the kilns and selected just the darkened bricks he wanted," Mr. Wagner said in the 1998 article.

James T. Wollon, a retired architect who lives in Havre de Grace, recalled Mr. Wagner's research on Mr. Ahlers.

"He brought architects together and gave us a tour of Loyola Blakefield, which Ahlers had designed," Mr. Wollon said. "He was fascinated and drawn to his work and his connections to the Roland Park Co."

Mr. Wagner was a former board member of the Friends of Maryland's Olmsted Parks & Landscapes. He conducted tours of the Guilford and Roland Park neighborhoods.

"Dean's legacy lives on in Original Northwood, as he had the vision and determination to make this neighborhood listed on the national registry," said Eric Lapointe, president of the Original Northwood Association.

In a 2009 Sun article, Mr. Wagner and his life partner, anthropologist Stefan Goodwin, described the annual arrival of a flock of crows in the community, a sign that winter was not far away.

"For a couple of weeks during the fall, large flocks of crows sometimes migrate through the beautiful old growth trees for an hour or so as the sky darkens," they said, adding that the birds "can occasionally be a bit noisy for a half-hour or so" but then move on, "leaving Original Northwood as peaceful as before."

Mr. Wagner remained an avid researcher of Baltimore's residential areas. He assisted in having numerous other places listed on the National Register, including Guilford, Dumbarton, Cedarcroft, Radnor-Winston, Tuscany-Canterbury, Lake Evesham, Homeland and Bellona-Gittings.

He also recently assisted in research on Druid Hill Avenue's Union Baptist Church in Upton, which he found was designed by New York architect William J. Beardsley.

In 2004, he married Dr. Goodwin, a retired Morgan State University department of sociology and anthropology chair. They had been partners for 22 years.

A memorial service will be held at 1:30 p.m. Saturday at the Doubletree by Hilton BWI, 890 Elkridge Landing Road in Linthicum.

Survivors include two daughters, Melanie Shafer of Lisle, Ill., and Madelyn S. Wagner of State College, Pa.; and his sister, Marilyn W. Hatch of Harrison, Maine. His two previous marriages ended in divorce.